Fe is the most abundant transition metal element in the human body and has crucial biological roles in oxygen transport, electron transfer, gene regulation, and macrophage polarization [20]. In biological systems, Fe exists predominantly in protein-bound forms such as hemoglobin, myoglobin, transferrin (Tf), and ferritin (FT) [21]. Fe plays a pivotal role in ferroptosis, including the formation of lipid peroxidase and catalytic intracellular redox reactions. Two ionic forms of Fe exist in the cell: ferrous Fe (Fe²⁺) and ferric Fe (Fe³⁺). The absorption, transport, storage, and utilization of these ions can influence the regulation of ferroptosis [22]. Under physiological conditions, one Tf molecule can bind two Fe³⁺ ions [23]. Tf binds to its high-affinity receptor 1 (transferrin receptor 1, TfR1) at the cell surface to form a complex that is internalized into endosomes. In the endosome, the six transmembrane epithelial antigen of prostat3 (STEAP3) reduces Fe³⁺ to Fe²⁺, which is then transferred into the cytoplasm via divalent metal transporter 1 (DMT 1) [24]. A small amount of Fe²⁺ forms an unstable, labile iron pool (LIP). LIP is at the core of Fe homeostasis and the regulation network. Fe²⁺ is transported to the outside of the cell by the action of membrane ferritransporter (FPN) [9]. Ferroptosis can be mediated by controlling FPN, thereby altering intracellular Fe²⁺ levels. Under normal conditions, Fe metabolism is in a balanced state [25]. Free cytoplasmic Fe²⁺ is introduced into FT and reoxidized to Fe³⁺ by the action of Fe oxidase present in isoferritin H. In eukaryotic cells, FT is a globular protein composed of 24 independent subunits that contain a defined amount of Fe³⁺[26]. FT is an Fe storage protein that occurs widely in living organisms. Its biological function is mainly in the participation of Fe metabolism, where it plays an important role in maintaining Fe balance and cellular antioxidants. The unique cage-like structure of FT allows it to store up to 4500 Fe atoms in its inner cavity. FT autophagy is a selective form of autophagy that helps to initiate the degradation of FT leading to ferroptosis. This triggers unstable iron overload (IO), lipid peroxidation, membrane damage, and cell death [27]. Mechanistically, lipopolysaccharide (LPS) increases the expression of nuclear receptor coactivator 4 (NCOA4) and the intracellular Fe²⁺ level, but decreases the level of FT. NCOA4-mediated FT autophagy transfers intracellular FT to autophagolysosomes for degradation and the release of free Fe. Hence, NCOA4 can interact directly with FT and degrade it in a FT autophagy-dependent manner, subsequently releasing large amounts of Fe. Cytoplasmic Fe²⁺ induces the expression of ferriomycin (SFXN1) in the mitochondrial membrane. SFXN1 then transports cytoplasmic Fe²⁺ into the mitochondria, where it generates reactive oxygen species (ROS) and causes ferroptosis [26]. Ferroptosis is therefore an autophagy process, and NCOA4-mediated FT autophagy supports ferroptosis by controlling cellular Fe homeostasis [28]. The depletion of FT and Tf leads to the accumulation of cellular Fe, which in turn produces ROS via the Fenton reaction, thus promoting cell ferroptosis.

Excess intracellular Fe²⁺ leads to the gradual accumulation of Fe-dependent lipid ROS, and eventually to the induction of ferroptosis [29]. At present, there are three known pathways involved in the production of Fe-dependent lipid ROS in ferroptosis [30]. First, due to its instability and high reactivity, Fe²⁺ combines with H₂O₂ to form a mixture [31] that oxidizes organic matter (alcohols, esters, etc.) via the Fenton reaction to generate ROS. The intracellular localization changes from the Golgi apparatus to the plasma membrane, where the PUFA reaction produces a large amount of ROS that leads to cell death [32]. This is a key step that drives ferroptosis and is currently also a very active area of research. Second, lipid auto-oxidation produces ROS, which is controlled by an Fe-catalyzed enzymatic pathway [33]. Third, an Fe-containing lipid synthase oxidizes arachidonic acid (AA) to produce ROS. The transfer of Fe from outside the cell to inside the cell is regulated by iron-response element binding protein 2 (IREB2) [34]. Knockout of the corresponding IREB2 gene can significantly reduce ferroptosis [35], thereby demonstrating the Fe-dependence of ferroptosis. Increased cellular Fe uptake via TfR1 reduces Fe overload through endosomal circulatory storage and the promotion of ferroptosis [36]. Inhibition of IREB2 has been shown to reduce the incidence of ferroptosis [37], and heat shock protein $\beta$1 reduces the intracellular Fe concentration by inhibiting TfR1 expression. However, it is still unclear how Fe homeostasis is dynamically controlled, and how abnormal changes in LIP levels give rise to a pathological state [38].

The specific mechanism by which ferrous ions expedite ferroptosis remains elusive. Current evidence suggests that compounds able to bind Fe to form a stable complex (Fe chelators) inhibit Fe ions from donating electrons to oxygen, thereby promoting the formation of ROS during ferroptosis [39]. Lipophilic Fe chelators and the Fe chelator deferoxamine (DFO) have attracted attention due to their distinct targets in ferroptosis [40]. The lipoxygenase (LOX) family, functioning as an Fe-dependent lipid reactive oxygen species (L-ROS) channel, can inhibit the degradation of glutathione (GSH) or GPX4 to block ferroptosis [41]. The active site of LOX requires the presence of Fe to exert catalytic activity, while the Fe chelating agents DFO and deferoxone can inhibit ferroptosis by extracting Fe from LOX [42]. Oxidized PUFA is a crucial component of LOX, promoting the further oxidation of Polyunsaturated fatty acids (PUFAs) into their hydroperoxide intermediates. The formation of soluble or lipid-free radicals instigates the initial cleavage or amplification of PUFA. ROS can induce lipid peroxidation by reacting with PUFA in the lipid membrane [43], with the level of PUFA being inversely proportional to lipid peroxidation. Based on the interaction between the membrane permeability of lipophilic Fe chelators and chelating Fe pools, PUFA can be produced in intracellular free Fe pools with ‘redox activity’ and can be inhibited by lipophilic Fe chelators [44].

Currently, the majority of ferroptosis mechanisms being investigated are associated with ROS [45]. The accumulation of intracellular ROS serves as a direct catalyst for ferroptosis, and numerous sources of lipid ROS can induce ferroptosis [46]. Fe²⁺ generates ROS through the Fenton reaction. The inactivation of GPX4 caused by GSH depletion, and nicotinamide adenine dinucleotide phosphate (NADPH)-dependent lipid peroxidation, can also lead to ROS accumulation. When GSH deficiency leads to inactivation of GPX4, the cells are primarily characterized by increased Fe-dependent lipid ROS production and PUFA consumption on the lipid membrane [47]. PUFAs are highly sensitive to oxidation by lipoxygenase and ROS, leading to the formation of lipid hydroperoxides (L-OOH). Under physiological conditions, GPX4 can reduce L-OOH to lipid alcohols (L-OH) and prevent the formation of lipid free radicals. When GSH deficiency leads to GPX4 inactivation, L-OOH forms toxic lipid free radicals (such as lipid alkoxy radica (L-O.)) with the participation of Fe ions. These free radicals simultaneously transfer protons to surrounding PUFAs, thus spreading oxidative damage from one lipid to another and ultimately leading to oxidative cleavage of PUFAs. When GPX4 is inactivated, the consumption of arachidonic acid (AA) can also induce ferroptosis [48]. Two lipid metabolism-related genes have been described: lysophosphatidylcholine acyltransferase 3 (LPCAT3), and acyl-CoA synthetase long-chain family member 4 (ACSL4). Ferroptosis is caused by ‘2’ ferroptosis inducers (FINs), such as Ras-selective lethal 3 (RSL3) and diphenyleneiodonium chloride 7 (DPI7) [49]. ACSL4 mediates the acylation of AA, while LPCAT3 catalyzes the acylation of AA to form membrane phospholipids, which can then transmit ferroptosis signals after oxidation [50]. AA-containing phosphatidylethanolamine is a key phospholipid that is oxidized and causes ferroptosis [51].

The reducing agent NADPH can maintain the reduced state of GSH and ensure the normal function of GPX4. Decreased NADPH activity interferes with the antioxidant effect of the GSH/GPX4 system, resulting in the accumulation of ROS [52]. In microglia, Fe ions can promote NADPH oxidase (NOX)-mediated ROS production, resulting in a significant decrease in the number and activity of neurons [53]. Pretreatment with the NOX2 and NOX4 inhibitors GSK2795039 and GKT137831 significantly reduced ROS production and neuronal damage [54]. NOX is also associated with NMDA receptor (NMDAr) activation and superoxide production through a mechanism closely associated with glutamate neurotoxicity. This mechanism is also involved in epilepsy and stroke. Excitatory toxicity was originally used to refer to rapid neuronal death caused by glutamate receptor activation, often attributed to Ca²⁺ influx via NMDAr. This resulted in the production of nitric oxide by neuronal nitric oxide synthase, and mitochondrial production of superoxide, which react to form highly cytotoxic peroxynitrite. The superoxide produced by NMDAr activation originates mainly from NOX, not from mitochondria. Neurons also produce superoxide during NMDAr stimulation, and the removal of superoxide prevents excitotoxic death. NOX is a multisubunit enzyme that uses NADPH-derived electrons from one side of the membrane to produce superoxides on the other side. The production of superoxide by NOX requires glucose, as this is a necessary substrate for the pentose phosphate shunt to regenerate NADPH from NADP+. In contrast, superoxides produced by mitochondria can be fueled by pyruvate or other non-glucose substrates. NMDAr and NOX signaling pathways involve Ca²⁺ influx, phosphoinositol-3-kinase, and protein kinase $\zeta$. Intervention at any of these steps can prevent superoxide production and excitotoxic damage [55].

System Xc– is a reverse amino acid transporter formed by the disulfide bond linkage of solute carrier family-7 member-11 protein with solute carrier family-3 member-2 protein [56]. This transporter mediates the exchange of cystine and glutamate. It serves as a crucial antioxidant system within the cell and establishes a functional pathway for the ferroptosis inhibitor erastin. System Xc– facilitates the exchange of extracellular cystine (Cys2) with intracellular glutamate at a 1:1 ratio. Cystine is synthesized into glutathione (GSH) under the catalysis of glutamate cysteine ligase (GCS) and glutathione synthetase (GSS) [57]. This pathway suggests that upon uptake, cystine is reduced to cysteine (Cys), which subsequently participates in the synthesis of GSH. The rate-limiting substrate for GSH synthesis is cysteine [58], while the rate-limiting enzyme is GCS [59]. Inhibition of GCS enzyme activity by buthionine sulfoxide interferes with GSH synthesis and induces cell death [60]. Fe chelators can mitigate cell death caused by thiophanate sulfoxide amine, indicating that inhibition of GSH synthesis can trigger ferroptosis [61]. GSH is a vital antioxidant in the human body and regulates normal physiological functions within a standard concentration range. Excessive GSH concentrations can lead to neurotoxicity [62]. When System Xc– is inhibited, the influx of cystine into the cell decreases, leading to a reduction in Cys levels and subsequently a reduction in GSH synthesis [63].

Glutathione peroxidases (GPXs) are a phylogenetically-related class of enzymes, with GPX4 being a member of this family [64]. As a reducing agent, GSH is an indispensable cofactor for GPX4 to manifest its antioxidant effects [65]. GPX4 catalyzes the conversion of GSH to oxidized glutathione (GSSG), while reducing intracellular toxic lipid peroxides (L-OOH) to their corresponding non-toxic lipid alcohols (L-OH). This process prevents the formation of Fe-dependent, highly reactive lipid alkoxy radicals (L-O.) derived from L-OOH. Consequently, GPX4 activity is vital for maintaining intracellular lipid homeostasis [66]. The inactivation of GPX4, or the silencing of genes related to GPX4 expression, results in the accumulation of lipid ROS and ultimately leads to ferroptosis [67]. Cells with down-regulated GPX4 expression were found to be more susceptible to ferroptosis, whereas cells with up-regulated GPX4 expression were resistant to ferroptosis [68]. GSH reduces ROS and active nitrogen species through the action of GPXs [69]. Glutathione-disulfide reductase (GSR) catalyzes the reduction of GSSG to GSH using electrons provided by NADPH/H⁺. Apart from its antioxidative role, GPX4 also plays a significant role in growth processes [70]. Chemical proteomics studies have confirmed that RSL3 is an affinity reagent for GPX4, and the triggering of ferroptosis by RSL3 has been speculated to depend on this affinity. The blocking of GPX4 activity by RSL3 is one of the reasons for RSL3-triggered ferroptosis [71]. However, the specific mechanism of action of RSL3 and other ‘class 2’ FINs on GPX4 remains unclear.

AD is an age-associated neurodegenerative disorder and a primary cause of cognitive deterioration in the elderly population [89]. This disease has emerged as a significant concern, impacting the health and quality of life of many individuals. Epidemiological investigations have revealed that the incidence of AD is as high as 10% in individuals aged over 65 years. The clinicopathological hallmarks of AD include senile plaques formed by extracellular $\beta$-amyloid (A$\beta$) deposition, neurofibrillary tangles resulting from abnormal Tau protein phosphorylation, synaptic dysfunction, and neuronal death [90]. While the precise etiology and mechanism of AD remain elusive, early-stage AD is characterized by the concurrent accumulation of A$\beta$ and elevated Fe concentration [91].

One of the characteristic pathological features of AD is the extracellular deposition of A$\beta$ in the cerebral cortex and hippocampus to form senile plaques. A$\beta$ is a byproduct of the cleavage of amyloid precursor protein (APP) by $\beta$-secretase and $\gamma$-secretase. Following the accumulation of cell matrix precipitation, A$\beta$ exhibits potent neurotoxicity. The increased A$\beta$ is the primary cause of neuronal damage and death [92]. Mutations in the APP gene can promote APP protein hydrolysis by $\beta$-secretase and $\gamma$-secretase, thereby increasing the production of A$\beta$ [93]. This facilitates further aggregation of A$\beta$ into amyloid fibers, thereby accelerating the pathological process of AD [94]. On one hand, the abnormal increase in brain Fe may play a significant role in the pathogenesis of AD by exacerbating the generation and accumulation of A$\beta$. On the other hand, the Fe in brain tissue is primarily derived from serum Fe transported into brain microvessels. Plasma Fe²⁺ and Fe³⁺ can interact with APP and A$\beta$, thereby increasing the accumulation of amyloid [95]. Moreover, the reduction of Fe³⁺ to Fe²⁺ by A$\beta$ can produce excessive free radicals and induce neuronal damage. Clinical studies have corroborated this, with researchers observing increased Fe content in the cerebral cortex, subcortical, and white matter regions of AD patients. Increased Fe content in the brain has therefore been speculated to play a crucial role in the pathological development of AD.

Glutamate excitotoxicity is also a significant pathogenic factor in AD. Additionally, trypsin can bind to protease-activated-receptor 2 (PAR-2), activate extracellular signal-regulated protein kinase (ERK) in the cortical neurons of AD mice, and counteract glutamate excitotoxicity. The Fe ion inducer erastin acts on the mitogen-activated protein kinase (MAPK) signaling pathway in tumors and can significantly increase phosphorylated ERK1/2. Brain tissue contains a substantial amount of unsaturated lipids, which are more susceptible to ferroptosis. Elevated levels of free radicals in the brain of AD patients create favorable conditions for lipid peroxidation [96], and lipid peroxide levels are significantly increased in brain regions that are rich in A$\beta$ oligomers [97]. Furthermore, A$\beta$ oligomers have been shown to integrate into lipid bilayers, thereby affecting the efficiency of free radical synthesis and hence the initiation of lipid peroxidation. In addition to being a critical step in ferroptosis, lipid peroxidation may therefore also play a crucial role in AD.

Plasma ceruloplasmin (Cp) is a multicopper oxidase with four active copper ions. Cp can oxidize Fe²⁺ to Fe³⁺, and reduce oxygen to water [98]. Moreover, Cp gene mutation and protein dysfunction are a significant cause of AD. Cp is involved in the binding of Fe³⁺ to transferrin and its transport in plasma. Reduction of Fe excretion by cells leads to excessive Fe²⁺ in the labile Fe pool and hence the production of hydroxyl radicals through the Fenton reaction. This in turn leads to ferroptosis and enhances the neuroinflammatory response through ROS, thus forming a complex cycle of exacerbation in AD patients.

Another pathological feature of AD is the excessive phosphorylation of Tau protein leading to the formation of neurofibrillary tangles (NFT) in neurons. Tau protein is associated with the stability of microtubules [99]. When the level of Tau phosphorylation is high, it first assembles into pairs of spiral filaments, and then aggregates and precipitates to form NFT. This causes microtubules to decompose, leading to neuronal death. Tau protein can regulate cellular Fe outflow through cell membrane transport. High phosphorylation and aggregation of Tau protein may impede this outflow and cause accumulation of neuronal Fe, thus further promoting the formation of NFT and creating a vicious circle. The imbalance of brain Fe homeostasis is closely related to Tau protein and NFT. Fe can regulate the phosphorylation of Tau protein and induce the accumulation of abnormally phosphorylated Tau protein [100]. Excessive Fe also promotes the phosphorylation of Tau protein, thereby promoting the production of NFT and ultimately leading to the dysfunction of neurons and synapses. Knockout of the Tau gene in rats can has been reported to produce age-dependent Fe accumulation and brain atrophy [101]. Abnormal deposition of Fe ions has also been observed in neuronal NFT. This may be related to the indirect involvement of Tau protein in the transmission of Fe ions in neurons during the pathogenesis of AD [102].

Recent studies have found that activation of lipoxygenase (LOX) is closely associated with the pathogenesis of AD, influencing the metabolism of A$\beta$ and Tau proteins, synaptic integrity, and cognitive function [103]. Studies have revealed that LOX expression is upregulated in the cerebral cortex and hippocampus of AD patients and animal models. Furthermore, LOX promotes the production of A$\beta$ by activating the cAMP response element-binding protein (CREB), and by regulating the beta-site APP-cleaving enzyme 1 (BACE1) [104]. Activation of cyclin-dependent kinase-5 (CDK5) induces hyperphosphorylation of the Tau protein, which can impair long-term potentiation, exacerbate synaptic dysfunction and precipitate cognitive decline, thereby advancing the progression of AD [105]. A possible role for LOX inhibitors in AD is supported by evidence that LOX-targeted intervention may be a promising strategy for the treatment of AD. The development of LOX inhibitors as anti-AD drugs therefore warrants further investigation. Inhibition of the specific pharmacology of LOX may also serve as an important approach to delay the progression of AD.

PD is a quintessential neurodegenerative disorder. It is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta and the formation of Lewy bodies and Lewy neurites, primarily composed of aggregated $\alpha$-synuclein ($\alpha$-syn) [106]. The etiology and pathogenesis of PD remain elusive, with a myriad of factors being potentially implicated including societal, pharmacological, and patient-specific elements. Clinical manifestations often encompass bradykinesia, myotonia, resting tremor, postural and gait abnormalities, cognitive/psychiatric disturbances, sleep disorders, autonomic dysfunction, and sensory impairments. The incidence of PD among individuals aged 65 years and above in China is approximately 1.7%.

Epigenetic alterations associated with the functional loss of SLC7A11 have also been identified in PD patients. This functional impairment leads to a reduction in cystine uptake, which subsequently causes a decrease in cysteine levels and culminates in the diminished production of GSH, thereby abrogating the ability of GPX 4 to mitigate lipid peroxidation [107]. Furthermore, the loss of DJ-1 function can compromise cysteine production via the sulfur transfer pathway, resulting in decreased GSH synthesis. The PLA2G6 mutation inhibits hydrolysis of the lipid peroxide 15-HpETE-PE, which would otherwise be decomposed by Fe²⁺ produced via the Fenton reaction or 15-LOX. Fe can post-transcriptionally up-regulate the translation of $\alpha$-synuclein (SNCA). The A53T mutation in SNCA causes an aberrant increase in Fe homeostasis by inhibiting the endocytosis of TfR1. This leads to Fe uptake through DMT1, oxidative stress due to increased cytoplasmic dopamine, and lipid peroxidation via the Fenton reaction. Current evidence suggests the mechanism of ferroptosis during the progression of PD may involve dopaminergic neurons. The human dopaminergic neuron cell line LUHMES exhibits high sensitivity to ferroptosis. These cells display pronounced characteristics of ferroptosis following administration of the ferroptosis inducer erastin.

The neurodegenerative disorder ALS is characterized by muscle atrophy and weakness, culminating in respiratory failure. Empirical evidence suggests the Fe chelator Trientine can extend the lifespan of a humanized ALS mouse model. This finding highlights the potential to exploit ferroptosis as a therapeutic target in ALS management. Other studies have found elevated levels of lipid peroxidation in the red blood cells of ALS patients and reduced GSH levels. The latter could exacerbate the degeneration of motor neurons in ALS [108].

An extended CAG triplet repeat sequence was found in the coding region of chromosome 4 in an HD patient and was originally labeled IT-15. This gene was later renamed HTT, and its protein product referred to as “Huntington’s protein”. Researchers have since focused on studying wild-type and mutant HTT proteins (mHTT), including elucidation of the mechanism by which mHTT causes HD, as well as the development of therapies that target mHTT and their biological effects [109]. mHTT expression leads to Fe accumulation in the brain of HD patients. Therefore, HTT levels and/or glutamine amplification within HTT are important regulators of Fe status. We previously showed that Fe does not directly interact with n-terminal HTT fragments, suggesting the effect of HTT on Fe is mediated by downstream effects in the Fe homeostasis pathway. Analysis of Fe homeostasis in R6/2 HD mice revealed decreased levels of iron reactive protein (IRP1 and 2), resulting in decreased TfR expression and increased levels of the neuronal Fe export protein ferritransporter (FPN). These changes were consistent with a compensatory response to an increase in the unstable Fe reservoirs within neurons [110]. The expression of N-terminal fragment containing mHTT-amplified polyglutamine (HTTQ94) can promote ACSL4-dependent and -independent ferroptosis. In addition, ALOX5 was found to be the main factor required for ACSL4-dependent ferroptosis induced by HTTQ94. Although ALOX5 is not required for the ferroptosis response triggered by common inducers such as erastin, the loss of ALOX5 expression prevents ferroptosis induced by HTTQ94-mediated ROS. ALOX5 is also required for HTTQ94-mediated ferroptosis in neuronal cells with high levels of glutamate. Thus, ALOX5 is critical for mHTT-mediated ferroptosis and may be a potential new target for HD [111]. Mitochondrial bioenergy dysfunction is also associated with neurodegeneration in HD. The brain tissues of human HD patients and mouse models of HD (R6/2 at 12 weeks and YAC128 at 12 months) showed elevated mitochondrial Fe, increased expression of the Fe-uptake protein mitoferrin 2, and decreased expression of the Fe-sulfur cluster protein frataxin. The mitochondria-enriched portion of mouse HD brain showed defects in membrane potential and oxygen uptake, as well as increased lipid peroxidation. In addition, the membrane-permeable, Fe-selective chelating agent deferrone (1 µM) could rescue these effects in vitro, but not hydrophilic Fe and copper chelating agents. This demonstrates the importance of Fe as a mediator of mitochondrial dysfunction and damage in a mouse model of human HD, and suggests that targeting the Fe-mitochondrial pathway may be protective [112].

During acute seizures, excessive ROS are produced due to mitochondrial dysfunction and/or increased NOX activity. The targeting of oxidative stress (OS), and specifically the antioxidant transcription factor nuclear factor erythroid 2-like 2 (Nrf-2), showed beneficial disease-modifying effects in models of acquired epilepsy by delaying the onset and progression of seizures. It does this by providing ROS to remove antioxidants, or by enhancing the endogenous antioxidant system. These effects may be facilitated by proteins involved in the production and circulation of GSH, the main intracellular antioxidant. Recent evidence from focal cortical dysplasia and nodular sclerosis clusters of congenital epilepsy suggests that OS and Fe metabolism are closely related and may work synergistically to exacerbate epileptic cell dysfunction and damage. Thus, high concentrations of unbound Fe²⁺ can act as a catalyst in Haber-Weiss and Fenton reactions to increase the potency of hydrogen peroxide to the more reactive ROS, thereby promoting cell dysfunction and death [113]. Direct and indirect evidence for neuronal ferroptosis in epileptic seizures has been obtained in several animal models of epilepsy. Importantly, the inhibition of ferroptosis has a neuroprotective effect [114]. The ferroptosis inhibitor FERstatin 1 (Fer-1) shows protective effects against acute seizures and memory loss. Fer-1 also inhibits ferroptosis-related markers in the hippocampus, including glutathione peroxidase (GPx) activity and the expression of 4-HNE protein. This suggests that Fer-1 may have a powerful therapeutic effect on seizures and cognitive impairment following post-traumatic epilepsy (PTE)-induced brain injury. It could therefore be a promising drug for the treatment of patients with PTE [115]. In addition, it has been suggested that uncontrolled repetitive generalized tonic-clonic seizures (GTCS), as described in refractory epilepsy, can cause hyperhypoxic stress in the heart. This induces hemosiderin-containing accumulation, as in iron-overload cardiomyopathy (IOC), and may be a hidden mechanism for the development of late arrhythmias leading to sudden unexpected death in epilepsy (SUDEP) [116]. Ferroptosis has also emerged as an important neuronal death mechanism in temporal lobe epilepsy (TLE), which is mainly affected by lipid accumulation and OS. REDOX changes in different organelles may have different pathophysiological significance during the course of Fe-death-related diseases. As a key organelle involved in ferroptosis, structural damage and the dysfunction of mitochondria can disturb energy metabolism and disrupt the excitatory/inhibitory balance, thereby increasing the susceptibility to seizures [117]. In addition, bioinformatics analysis was used to construct the complex network, drug network, mRNA-miRNA network, and transcription factor network for three key genes, namely HIF1A, TLR4 and CASP8. This provides a framework for exploring potential regulatory targets and possible mechanisms of ferroptosis in epilepsy, thereby providing new insights into the treatment of epilepsy [118].

Recent studies have highlighted a strong link between ferroptosis and stroke. Intracellular Fe overload is pivotal to ferroptosis. Ferroptosis has been shown tp be involved in neuronal death after ICH in vitro and in vivo, and it also plays an important role in early brain damage after SAH. Ischemic stroke involves two important events, ischemia and reperfusion injury (IRI), which can result in severe cell damage and poor prognosis. After ischemia, Fe accumulation occurs due to the inhibition of tau expression. The excess Fe flows into brain parenchyma via the damaged blood-brain barrier (BBB) where it promotes ROS production through the Fenton reaction. This subsequently promotes nuclear, proteome and membrane damage, and eventually triggers cell death by ferroptosis [119]. Following severe ischemic and hypoxic brain injury, Fe deposition increases in the basal ganglia, thalamus, periventricular, and subcortical white matter areas. In a mouse model of ischemic stroke, GSH levels in neurons were found to be significantly reduced, lipid peroxidation enhanced, and GPX4 activity reduced. GSH and GPX4 are key regulators of ferroptosis and are strongly associated with hemorrhagic and ischemic stroke. In addition, the use of ferroptosis inhibitors significantly improved the outcomes of patients with ischemic stroke. Studies of hemorrhagic stroke showed that n-acetylcysteine (NAC) inhibits the heme-induced ferroptosis of brain cells by neutralizing toxic lipids produced by AA-dependent ALOX5 activity. The early application of NAC after intracerebral hemorrhage can reduce neuronal mortality and improve prognosis. Other studies have reported a significant decrease in GPX4 expression in brain tissue 24 h after intracerebral hemorrhage. Increased GPX4 expression after intracerebral hemorrhage can significantly reduce neuronal dysfunction, brain edema, BBB damage, OS, and inflammatory damage. Application of the ferroptosis inhibitor Fer-1 after intracerebral hemorrhage also significantly reduces the degree of secondary brain injury [109]. In addition, neurovascular units (NVU) play a key role in the occurrence and development of ischemic stroke, and the function of NVU in stroke development can be modulated by activating or inhibiting ferroptosis [120].

Electroacupuncture therapy (EA) has been shown to inhibit the Xc-/GSH/GPX4 axis of the System after traumatic brain injury (TBI) by upregating the expression and activation of xCT, which is a major functional subunit of System Xc-. This confirms the notion of an EA effect in the treatment of TBI and provides theoretical support for its application in clinical practice [121]. Moreover, autophagy may be a viable therapeutic strategy for ischemic stroke, providing neuronal protection, reducing brain damage, and benefiting ischemic peripheral brain tissue [122].

Neurodegeneration with brain iron accumulation (NBIA) is a group of inherited neurological disorders characterized by significant genetic heterogeneity and in which Fe atypically accumulates in the basal ganglia. This results in changes in the brain visible by magnetic resonance imaging, histopathological abnormalities, and neuropsychiatric clinical symptoms. Mitochondria play an important role in NBIA disease, and an NBIA subtype with altered mitochondrial proteins is considered to be a mitochondrial disease with compromised oxidative phosphorylation. NBIA patients with defective Pank2, Coasy, Pla2g6, or C19orf12 genes exhibit widespread Fe accumulation in the globus pallidus and substantia nigra, as well as mitochondrial disorders and neurological or motor disorders [123]. $\beta$-propeller protein-associated neurodegeneration (BPAN) is a subtype of NBIA caused by loss-of-function variants in WDR45. According to the International NBIA and Related Disease Registry, 40-45% of NBIA is caused by BPAN, and WDR45 deficiency can affect FT autophagy and ferroptosis, thus interfering with Fe recovery [124]. In addition to Fe accumulation, the NBIA phenotype also shows corresponding pathological changes in tau protein in AD, and synuclein in PD [125].

The Cyst(e)ine/GSH/GPX4 axis has long been recognized as a pivotal mechanism in the regulation of ferroptosis [126]. Inhibition of the cystine-glutamate antiporter, inhibition of GSH production, and reduced expression or activity of GPX4 can directly influence the initiation and progression of ferroptosis. GSH is a tripeptide composed of glutamic acid (Glu), cysteine (Cys), and glycine (Gly), in which the cysteine sulfhydryl functional group is an antioxidant. The cysteine for GSH can be obtained from methionine via the trans-sulfur pathway, or from extracellular cystine via System Xc–. The selenoprotein GPX4 is a key antioxidant enzyme that can directly reduce phospholipid peroxides to phospholipid hydrogen peroxide. The biosynthesis of GPX4 depends on co-translational incorporation of selenocysteine (Fig. 3, Ref. [127]) [128]. Cysteine and homocysteine inhibit ferroptosis in a GPX4-dependent manner. However, cysteine inhibition of ferroptosis is not associated with GSH synthesis, and homocysteine can inhibit ferroptosis through both non-cysteine and non-GSH pathways [129].

Fig. 3.

The regulation of ferroptosis. Multiple pathways inhibit ferroptosis by resisting oxidative stress and inhibiting lipid peroxidation. These include the system Xc–/GSH/GPX4, FSP1/CoQ10, GCH1/DHFR/BH4, DHODH/CoQ, and p62/Keap1/Nrf2 pathways (Reproduced with permission from Sun Y, et al., Mechanisms of Ferroptosis and Emerging Links to the Pathology of Neurodegenerative Diseases; published by Frontiers in Aging Neuroscience, 2022 [127]). TFRC, transferrin receptor; FTL, ferritin light chain; FTH, ferritin heavy chain; ARE, antioxidant response element; NAD(P)H, reduced nicotinamide adenine dinucleotide (phosphate); IPP, isopentenyl pyrophosphate; IPF, isopentenyl transferase; SEC, selenocysteine; DHODH, dihydroorotate dehydrogenase; DHO, dihydroorotate acid; OA, orotate; GSSG, oxidized glutathione; DHFR, dihydrofolate reductase; $\alpha$-TOH, $\alpha$-tocopherol; GTP, guanosine triphosphate; DHFR, dihydrofolate reductase.

Coenzyme Q10 (CoQ10), also known as ubiquinone, is a lipophilic metabolite derived from the mevalonate pathway. Extramitochondrial CoQ10 is regenerated by fibroblast-specific protein 1 (FSP1). FSP1 is thought to have a pro-apoptotic role under certain conditions. It can also be transferred to the nucleus through the cytoplasm or mitochondria, causing DNA degradation [130]. The FSP1/CoQ10 pathway acts in parallel with the System Xc–/GSH/GPX4 pathway. The anti-ferroptosis function of FSP1 is based on its oxidoreductase activity and uses NAD (P) H/H⁺ to reduce extra-mitochondrial CoQ10 to ubiquinol. Panthenol can act as a strong radical and trap antioxidant to directly reduce lipid radicals, or indirectly block lipid peroxidation through $\alpha$-tocopherol, a common form of vitamin E [18].

GCH1/BH4/DHFR is a GPX4-independent mechanism of ferroptosis inhibition [131]. It is also an important part of the antioxidant system and can reduce the OS response. GCH1 is a cyclic hydrolase of guanosine triphosphate and a rate-limiting enzyme for BH4 synthesis. The GCH1-BH4-phospholipid axis acts as a major regulator of ferroptosis. It controls endogenous production of the antioxidant BH4, the abundance of CoQ10, and selectively inhibits phospholipid consumption containing two polyunsaturated fat acyl tails, thereby inhibiting ferroptosis. This demonstrates a unique ferroptosis protection mechanism that acts independently of the Cyst(e)ine/GSH/GPX4 mechanism [132]. BH4 is an effective free radical antioxidant, and as such is oxidized into dihydrobiopterin (BH2). BH2 can be regenerated into BH4 using NADPH as a hydrogen donor under the catalysis of dihydrofolate reductase (DHFR). BH4 biosynthesis is an important compensatory pathway under conditions of GPX4 inhibition [131]. Folic acid (FA) is important in the treatment of a variety of neurological diseases. The mechanisms for FA supplementation include inhibition of the transcription factor Sp1 (thereby inhibiting GCPII transcription), reducing Glu content, and blocking cell ferroptosis [133]. Liver cells treated with methotrexate (MTX) experience ferroptosis, and this can be attenuated by ferroptosis inhibitors [134]. MTX is a folate antagonist that inhibits the conversion of dihydrofolate into bioactive tetrahydrofolate, thereby inhibiting the synthesis of purine and pyrimidine by binding to DHFR in cells. DHFR is therefore an important regulator of ferroptosis. It regenerates oxidized BH4 with MTR to genetically or pharmacologically block DHFR function, and in conjunction with GPX4 inhibition can induce ferroptosis [131].

Dehydrogenase (DHODH) is one of the rate-limiting enzymes for the de novo synthesis of pyrimidine. It is located in the inner mitochondrial membrane and catalyzes the oxidation of dihydroorotic acid to orotic acid. During this process, electrons are transferred to CoQ on the inner mitochondrial membrane, thereby reducing it to the antioxidant panthenol and inhibiting ferroptosis in cells with low GPX4 expression [135].